A SPECIAL unit at the De partment of Investigation formed just a year ago to examine nonprofit agencies with city contracts has opened a startling 30 to 40 cases involving fraud, The Post has learned.

“I’m glad we cast this net – we got a big load of fish,” said DOI Commissioner Rose Gill Hearn, who launched the unit in response to a 2006 scandal at the Gloria Wise Boys & Girls Club, where two top executives ended up pleading guilty to misappropriating $1.2 million.

“It struck me, this is not a single case,” Gill Hearn added. “It’s a symptom of a lot of other problems. No one is watching our money.”

Acting solely on complaints from whistleblowers, four expert investigators have turned up some eye-popping evidence of rip-offs.

“We’re not really doing random audits,” Gill Hearn explained.

“Typically, an insider in some bookkeeping capacity comes forward [and says], ‘I’ve been asked to create an invoice as if we really did purchase certain items for this after-school program that we didn’t.’

“Or, ‘So and so renovated his condo, and I had to pass the checks through for that.’ As you can imagine, people get scared. They know it’s criminal, but they’re told they have to do it. What do you do? Some people call us.”

Gill Hearn declined to discuss specifics.

But she said all the cases could end up in criminal prosecutions and noted that she is working with the US Attorney’s offices, the district attorneys and state Attorney General Andrew Cuomo.

“This is fraud. This is misappropriation. This is nepotism. This is self-dealing,” Gill Hearn declared.

“Underlying it are members of the board [of directors] asleep at the switch, not paying attention to sound fiscal controls and their fiduciary responsibility.”

In addition to outright fraud, DOI is also looking at nonprofit executives with “big, inflated salaries” and questionable “personal expenditures being paid for with what is city contract money,” Gill Hearn said.

“We’re taking a look at a lot of shades of gray.”

One nonprofit executive confided to The Post that he has been troubled for years by a practice of some agencies that is perfectly legal as long as it is disclosed: engaging in business dealings with board members.

“They should resign if they want to do business with their own agency,” the executive said.

Although all city contracts are routinely audited, the deals with the nonprofits haven’t – until now – been subject to the type of scrutiny that is routine for city agencies.

“There’s a fallacy out there that an audit catches [potential wrongdoing],” one insider said. “But it’s very hard to pick up collusion between an executive director and a board chair.”

The city spent $3.8 billion last year on human-service contracts, which included home care.

Mindful of the impact of her investigations, Gill Hearn said she is for the first time sharing information about potential criminal matters with city agencies so services to the neediest aren’t disrupted.

“I’m not interested in shutting down a not-for-profit where there’s just one bad apple and the program overall is a valuable program,” she said.

In fact, Gill Hearn said she has met with board members, chief financial officers and CEOs of many nonprofits that are performing valuable services for the city’s most vulnerable citizens.

“I’m a full-blown member of that team. I get it,” she said. “I’m their biggest fan.”

Michael Clark, executive director of the Non-Profit Coordinating Committee of New York, which represents nearly 1,600 nonprofits, said his members would welcome strengthened enforcement to root out corruption.

“No one is damaged more painfully on a regular basis [by corruption] than the thousands of nonprofits where people work their butts off,” he said. “This just drives us nuts.”

In the Gloria Wise case, a director and a deputy director of the agency, which had served The Bronx since 1977, diverted funds intended for children and the elderly to buy cars, furniture and renovations to a beachfront apartment, as well as to loan $875,000 to the Air America Radio network.